我更新了源，也添加了DNS，但还是无法进行update，代码如下：

(base) ruoruo@DESKTOP-5SC16P5:/etc/network$ sudo cat /etc/resolv.conf

This file was automatically generated by WSL. To stop automatic generation of this file, add the following entry to /etc/wsl.conf:

[network]

generateResolvConf = false

nameserver 8.8.8.8
nameserver 8.8.4.4
(base) ruoruo@DESKTOP-5SC16P5:/etc/network$ sudo apt-get update
Err:1 http://mirrors.tuna.tsinghua.edu.cn/ubuntu focal InRelease
Temporary failure resolving 'mirrors.tuna.tsinghua.edu.cn'
Err:2 http://mirrors.tuna.tsinghua.edu.cn/ubuntu focal-updates InRelease
Temporary failure resolving 'mirrors.tuna.tsinghua.edu.cn'
Err:3 http://mirrors.tuna.tsinghua.edu.cn/ubuntu focal-backports InRelease
Temporary failure resolving 'mirrors.tuna.tsinghua.edu.cn'
Err:4 http://mirrors.tuna.tsinghua.edu.cn/ubuntu focal-security InRelease
Temporary failure resolving 'mirrors.tuna.tsinghua.edu.cn'
Reading package lists... Done
W: Failed to fetch http://mirrors.tuna.tsinghua.edu.cn/ubuntu/dists/focal/InRelease Temporary failure resolving 'mirrors.tuna.tsinghua.edu.cn'
W: Failed to fetch http://mirrors.tuna.tsinghua.edu.cn/ubuntu/dists/focal-updates/InRelease Temporary failure resolving 'mirrors.tuna.tsinghua.edu.cn'
W: Failed to fetch http://mirrors.tuna.tsinghua.edu.cn/ubuntu/dists/focal-backports/InRelease Temporary failure resolving 'mirrors.tuna.tsinghua.edu.cn'
W: Failed to fetch http://mirrors.tuna.tsinghua.edu.cn/ubuntu/dists/focal-security/InRelease Temporary failure resolving 'mirrors.tuna.tsinghua.edu.cn'
W: Some index files failed to download. They have been ignored, or old ones used instead.
(base) ruoruo@DESKTOP-5SC16P5:/etc/network$

首先，确保您的 WSL2 Ubuntu 20.04 系统已经安装了 update 工具。您可以在终端中运行以下命令来安装它:
sudo apt-get update
sudo apt-get install wsl2-client
然后，您可以使用 WSL2 Ubuntu 20.04 内置的 update 工具进行更新。在终端中运行以下命令:

sudo apt update
sudo apt install apt-transport-https
curl -s https://packages.microsoft.com/config/ubuntu/18.04/packages-microsoft-prod.deb -o /etc/apt/sources.list.d/packages.list
sudo apt-get update
sudo apt-get install WSL2-Ubuntu
这将更新您的 WSL2 Ubuntu 20.04 系统，并安装最新版本的 WSL2 Ubuntu。http://www.7zhan.net/

最后，您可以重新启动您的 WSL2 Ubuntu 20.04 系统，以便更新生效。在终端中运行以下命令:
sudo systemctl restart wslf2